This invention relates to the froth flotation separation of sulfide minerals from their ores and, more specifically, concerns the depression of undesirable gangue comprising mainly siliceous materials in the froth flotation of complex metal sulfide ores for the concentration of zinc sulfide.
In the recovery of mineral concentrates from ores by froth flotation, particularly of zinc sulfide concentrates from comminuted complex sulfide ores, the ores typically are subjected to a number of operations in interconnected flotation circuits often including crushing, grinding, and regrinding of intermediate flotation products. These operations ultimately result in separation of the gangue in tailing fractions and the formation of concentrates predominant in the desired mineral such as zinc sulfide.
The flotation circuits typically include one or more rougher, cleaner and recleaner flotation stages with conditioning of the feed thereto by reagents selected to effect separations between desired mineral species and from undesired gangue. These reagents comprise collectors, depressants, activators, deactivators, frothers and the like. The depressants include a depressant for gangue material which contains, for example, silica, quartz, lead or iron silicates or the like. The gangue depressant is added to feed slurry at one or more points in the flotation circuit separate from or together with other reagents. The amount of depressant employed is dependent on the amount of gangue in the feed to the flotation circuit, and to some extent also on the amount of zinc sulfide in the feed. This gangue, if not removed, would interfere severely with subsequent processing of the zinc sulfide concentrate, such as in the roasting, leaching or electrowinning. Consequently, the level of the gangue as measured by silica content in the concentrate should be limited to below about 1.5% by weight of the dried solids, higher levels of gangue rendering the concentrate unsuitable for efficiency recovery of zinc.
Gangue depressants known to the art include carboxymethylcellulose and ethylcellulose, glue, gelatin, acid, starch and dextrin. Also, A. M. Gaudin (Flotation, 2nd Ed., McGraw-Hill, 1957) mentions that silica or quartz can be deactivated by soda ash, sodium silicate or an alkali phosphate, and that other agents occasionally found useful are tartrates, citrates and dyes, especially highly hydroxylated hydroquinone dyes. A. F. Taggart (Handbook of Mineral Dressing, John Wiley & Sons Inc., N.Y., 1945) mentions several reagents for depressing silica and silicates in mineral flotation. Additional disclosures of depressants are as follows: U.S. Pat. No. 4,220,525 teaches that polyhydroxy amines are useful as depressants for silica, silicate, carbonate, sulfate and phosphate gangue materials; U.S. Pat. No. 4,339,331 teaches that nonsulfide materials are depressed with a crosslinked starch or starch-containing substance having anhydroglucose cross-linking units; U.S. Pat. No. 2,919,802 discloses that mannogalactan is useful as a depressant for slimes and in particular that an alkali metal phosphate or silicate is a depressant for slimes that accompany sulfide ores; and U.S. Pat. No. 2,373,305 discloses that citric acid, tannic acid or quebracho are useful as gangue depressants.
These known depressants are often found to be effective only in the treatment of certain specific ores due to the presence of salts in the water, the characteristics of ionic impurities associated with the siliceous gangue materials and other empirical factors, poorly understood.